The present invention relates to an image processing method and apparatus therefor, and more particularly to an image processing method and apparatus therefor capable of image processing at high speed and suitable for realizing a compact apparatus.
In an image processing apparatus which obtains a distinctive and clear image with no noise by processing an unclear original image with noises, a matrix calculation is performed based on the value of an objective pixel to be image processed in an original image and on the values of neighborhood pixels, to thus determine a new value of the objective pixel.
Various types of conventional image processing apparatus for performing an operation (hereinafter called a neighborhood operation) are known wherein the value of a pixel to be processed, i.e., an objective pixel and the values of neighborhood pixels supplied as input data are calculated to determine an output value of the objective pixel. In the meantime, original image data are generally arranged consecutive in the column direction (i.e., in a line direction) within the address space of an image memory. Therefore, the addresses of the original image adjacent in the row direction (i.e., in the direction perpendicular to the line) are different by a certain amount in most cases. In a neighborhood operation, the values of neighborhood pixels are read from the image memory, stored in a buffer, and thereafter supplied to a processing unit. Therefore, it becomes necessary to access the image memory several times until all the neighborhood pixels necessary for a neighborhood operation for one objective pixel have been read. Therefore, it may occur that in a neighborhood operation for another pixel, the addresses used in the previous operation are again accessed, resulting in a number of accesses and in a long process time.
To solve this problem, according to a conventional method, for example, as disclosed in IEEE, Computer, November, 1981, pp. 53 to 67, the number of accesses is reduced taking into consideration the fact that the difference between the address of one pixel and the address of adjacent pixel at a different line is constant throughout any position of the lines if an image to be processed is present in a rectangular frame. This method prepares an additional temporary memory (e.g., shift register) for storing a series of pixels necessary for matrix calculation. Original image data are sequentially read from an original image memory one word (one address unit) after another in the column direction. The read-out data are shifted in synchro with data processing to thus automatically derive neighborhood pixels. According to this method, it is possible to access all addresses of an original image once for each address without duplicate accesses. However, if for example a 3.times.3 pixel matrix calculation is applied, eight consecutive pixels are required as the neighborhood pixels. Therefore, it becomes necessary to use a temporary memory whose capacity corresponds to 2 lines and three pixels.
According to other prior art not using such a line memory, a same address of an original image memory is required to be accessed plural times, thus posing a problem of a long transfer time of image data.
In contrast with the above, the prior art using a line memory shown in the above-described publication accesses a same address of an original image memory only one time so that data transfer time becomes short. However, for a 3.times.3 matrix calculation for example, line memory in excess of 2 lines becomes necessary. Therefore, the memory capacity becomes large, and in addition a complicated control circuit for the line memory is needed.